THYROTROPIN STIMULATES THE EXPRESSION OF AN ACIDIC RIBOSOMAL-PROTEIN, P0, MESSENGER-RIBONUCLEIC-ACID IN CULTURED RAT-THYROID (FRTL) CELLS

Acidic ribosomal proteins, P0, P1, and P2 in eukaryotic 60S subunits play an important role in polypeptide chain elongation during the translational step. To investigate the role of TSH in protein synthesis in the thyroid, we examined the effect of TSH on ribosomal P-protein biogenesis in FRTL cells. First, we investigated the influence of TSH on P0-protein gene expression. RNA slot blot hybridization revealed that the effect of TSH on P0-protein mRNA accumulationin the quiescent FRTL cells was time- and dose-related. This stimulatory effect of TSH was mimicked by (Bu)2cAMP. Nuclear run-off transcription assays revealed that TSH increased the transcriptional activity of the P0-protein mRNA without an increase in beta-actin transcriptional activity. On the contrary, the stability of P0-protein mRNA decreased after the addition of TSH. Cycloheximide markedly inhibited TSH-induced P0-protein mRNA accumulation in FRTL cells. Second, using a synthetic oligonucleotide probe, we have shown that TSH also increased P2-protein mRNA levels in FRTL cells. Furthermore, immunodetection of P-proteins using anti-P-protein antibody showed that TSH significantly increased the amount of P-proteins in the cells. These results suggest that TSH can increase the amount of acidic ribosomal P-proteins at least in part through an increase in the level of P-protein gene transcripts. This effect occurs via a transcriptional mechanism and requires ongoing protein synthesis. Thus, TSH might play an important role in ribosome biogenesis in FRTL cells.